When I mouse over someone a big box pops up with random info about the player and I’d like to disable it, but I don’t know what it’s called.
The tooltip?
the system GameTooltip tends to live in the bottom right, but it doesnt usually have much info about other players when you mouseover them so it sounds like you have a mod installed thats adding a whole bunch more info to it.
standard procedure is to disable half you mods and see if it goes away, if it does then its in that lot, if not its in the other half. just keep breaking those up in half until you can identify it.
failing that provide a screenshot of the tooltip or a list of addons and someone may be able to work it out.